Amyloplast Formation and Starch Granule Development in Hard Red Winter Wheat

Abstract

Plastids in the coenocytic endosperm of young wheat caryopses were mostly in the form of pleomorphic proplastids with a few of the plastids containing small starch granules. Following cellularization of the coenocytic cytoplasm, the outer one or two endosperm cell layers became meristematic and continued to divide until about 14 days after flowering (DAF). During the first week of endosperm development, newly divided cells had plastids that were pleomorphic in shape, while subaleurone cells interior to the meristematic region contained amyloplasts that contained a single‐size class of starch granules (incipient A‐type starch granules). The pleomorphic plastids exhibited tubular protrusions that extended a considerable distance through the cytoplasm. Amyloplasts in cells interior to the meristematic region did not exhibit protrusions. Both subaleurone and central endosperm cells had amyloplasts that exhibited protrusions at 10–12 DAF, and some of the protrusions contained small starch granules (incipient B‐type starch granules). Protrusions were not observed in endosperm amyloplasts at 14 DAF. Two sizes of starch, large A‐type and smaller B‐type granules were present within the cells, however. Amyloplast protrusions were numerous again at 17 DAF in both subaleurone and central endosperm cells; at 21 DAF, a third size class of small C‐type starch granules was observed in the cytoplasm. Amyloplasts in the endosperm of wheat apparently divided and increased in number through protrusions because binary fission typical of plastid division was never observed. Protrusions were observed in the coenocytic cytoplasm, in dividing cells, in subaleurone and central endosperm cells at 10–12 DAF, and in subaleurone and central endosperm cells at 17 DAF. The results suggest that there are three sizes of starch granules produced at specific times during wheat endosperm development.

Isolation of differentially expressed genes in wheat caryopses with contrasting starch granule size

“…There are two distinct classes of starch granules based on their size and timing of formation in wheat endosperm [6,7,21] with a temporal transformation in the size distribution of starch granules during wheat endosperm development. The formation of the A-type starch granules initiates around 4-14 days DPA, when the endosperm is still actively dividing [5,21], whereas B-granules are initiated at about 10-16 DPA in stromules [22].…”

“…The starch granules, designated A-and B-type [5], can be distinguished based on size, shape, relative proportion, and the timing of their initiation in the endosperm, a process which, presumably, is under a defined genetic program. C-type starch granules have also been reported in wheat [6,7]. Differences in starch granule composition [8] and their molecular structure [9] have been reported to play an important role in product application [10].…”

Defoliation Influences Starch Granule Distribution and Structure in Medicago sativa L. Taproots as Revealed by SEM and TEM

“…Three different class sizes of starch granules have been described: A, B, and C types [10]. Some species appear to synthesize two or all three class sizes of starch granules although at different times [10].…”

“…Three different class sizes of starch granules have been described: A, B, and C types [10]. Some species appear to synthesize two or all three class sizes of starch granules although at different times [10]. Type A class occurs mostly in cereal endosperm and is large (>15 µm) [10] consisting of regions of densely packed double helix [11].…”

“…Some species appear to synthesize two or all three class sizes of starch granules although at different times [10]. Type A class occurs mostly in cereal endosperm and is large (>15 µm) [10] consisting of regions of densely packed double helix [11]. Type B class size is medium (5-15 µm) occurring in wheat endosperm [10], leaf and tuberous tissues [11].…”